How is it any different from taxiing out on one engine like we do already and then having start problems starting #2 or #3 or #4?

Just like anywhere else if an aircraft has issue while on the taxi out then you get parked in the penalty box, de-ice pads or elsewhere.

Personally though I can see the concept of electric motors on the wheels for ground taxi being a better solution than the logistics of tugs in the long term, just my own opinion without any solid data to back it up at all.

Hybrid car electric motors operate in a different way which doesn't involve the issue of having a connected wheel spinup from 0 to 250 km/h in 0.4 seconds upon impacting a concrete surface at up to 150 metres per second vertically, so it is improbable that they could ever venture into this area.

Interlocks and relays can and do fail. So I imagine there would be a lot of engineering development work and risk matrix work required before it became practical. Is it worth the expense? I don't know. Airlines have refused to wear the development and ongoing maintenance cost for things far less complicated than that!

Single engine taxi before departure is very common in the US especially at busy airports and flying to busy airports where there is flow control even before you take-off. On the ERJ175s, we need 2 minutes after engine start before we can take-off. It's usually never a problem. I'm surprised it's not so common in other parts of the world.

Totally missing the point. They are talking about using them for taxi only. I.e. Clear the runway, after landing checklist then shutdown the engines. So there's no reason for the motors to spin up at all until the aircraft is already at a complete stop and off the runway.

Ever heard of a freewheel unit?

Not that I really care, I'll happily keep burning fuel, but to say it's not do-able at all is a little closed minded.

The economics are very simple. Single engine taxiing saves money. The more flights you do, the more you save. If you have a start problem then that is tough but really, ho many start problems have you had? My company have been doing it for near enough 12 years without a problem (100,000 flights per year). I'll also suggest that as soon as the economic case for having electric taxi motors is clear, airlines will fall over themselves to get them installed. Complexity is someone else's problem, looking after cash is theirs.

PM

Here's an idea - electric pilot-controlled tugs that self-drive back to base via a tiny tug-only taxiway.

Someone do eeeeetttt!

Even better, they self drive in a tiny tunnel that doesn't need much ventilation etc, basically a tube / pipe.

OP...

The amount of aircraft doing SE taxi is dynamic. This changes on a flight by flight basis dependant on a number of factors, predominantly taxi time. Once the APU is up and running and a sufficient cool-down period is completed (3 minutes for us), then the option to conduct SE taxi is there.

I'm yet to see anyone take it up taxiing out and imagine that the only time it would be is when the time to take-off is significant (above 30 minutes). In this case I would also suspect both engines would be started initially, and provided it's a normal start then would proceed to shut one down (and eventually restart) after being notified that the time to take-off would be extensive. I assume the provision is there to accommodate 'unusual' situations or for airlines running out of busier airports (Heathrow?) where taxi times are consistently long.

As for taxiing in, we burn 1.2 tonne/hour at idle (B767, two-engines), so discounting the extra fuel for the APU and the higher power settings for crossing runways or getting onto the bay/during turns, I guess 2 minutes you're looking at 60kg of gas saving per time we do it.

Hope this helps. :ok:

In the USA normal practice is to taxi out on one engine until you see how long the line is. About 4-5 aircraft before your turn to take the runway then start remainder of engines with enough time to meet warm up limitations.

After landing taxi in on one after meeting cool down requirements, unless there's tight turns into the gate.

Curious novice here. Despite fuel burn being a non-issue in this scenario can somebody explain why its taboo to move say a Seminole from one part of an airport to another on one engine?

Probably because it's quicker to move it. And a secondary being that most piston engine wear is done in the first minute of start, so why start it for only a couple of minutes if you don't need to.

It's not taboo. They are not often used by commercial airlines run by bean counters. So nobody bothered to write a procedure for it and have it approved...

I tried to single-engine taxi a Duchess once after a starter motor failure. Couldn't do it.

That was indeed my point.

And of course I'm not saying it's not do-able. I'm saying that the engineering and development effort with all the considerations required is highly unlikely to be cheap and easy.

It's not being closed minded, just realistic. Of course it is possible. But is it worth it? There are many risk vs reward considerations.

You can make an economic case for anything. My airline famously made an economic case for only using idle-reverse thrust on landing until it ran a perfectly serviceable Boeing 747 full of passengers off the end of a runway into a golf course. The aircraft was as near to a write-off as you can get, without actually being written off (the decision to repair raised eyebrows in some circles), then we spent the next 15 years using full reverse thrust on all landings.

How good do people reckon the economics were there?

You can make economic cases for instantaneous fuel savings for many things but you have to balance operational and engineering risks too, so it's just not that simple. Over my 30 year career I've not once ever seen a bean-counter who understands what "operational" or "engineering" actually means but I've seen quite a number of fuel-saving decisions reversed, reversed back again, then reversed back again, then reversed back again, etc. They sit at a desk (be surprised if they even have a window) and deal with numbers.

We had a scenario not long ago where one department in the airline made a decision to stop washing fuselages and compressors because it was expensive and it had no bearing on flight safety (true), and helped them meet their KPIs. It cost flight operations many millions of dollars in fuel penalties due to performance factor increases. Took something like 6 months after the supporting data was gathered to get it reversed, but in the meantime multiple millions of dollars fluttered away, never to return. Amazing how tenaciously senior managers hang on to their KPIs.

The whole thing is an absurd game. But I just fly the things.

Some airlines introduced s/e taxy after landing only to find engine maintenance increased due to bearing wear. If you want to reduce trip fuel put some pilots and cabin crew on a diet.

Enjoyable conversation but any ideas on the number of wide body jets and the number of narrow body jets in the QF group and how many sectors they average a day?

Here ya go:

TaxiBot Now Certified on Airbus A320 Family | AviationPros.com

Funny thing is that one of the analysts in American Airlines recently said that 80% of our fuel saving are simply by flying the dispatch release/flight plan as it's actually planned. The remainder is from single engine taxi etc